Despite advances in knowledge about tooth morphogenesis and differentiation, relatively little is known about the molecular basis of the induction of tooth formation. My recent studies show that upon epithelial deletion of Ape or activation of Wnt/(3-catenin signaling, adult oral tissues, especially young adult tissues, retain odontogenic potential and can still form new teeth, indicating that Ape and Wnt/p-catenin are key regulatory genes in tooth induction. Moreover, I have found that the induction of supernumerary teeth by Ape deficiency occurs through activation of Wnt/p-catenin signaling. Once initiated, the development of these new teeth proceeds autonomously to stages of cell differentiation and root formation. My long-term goal is to elucidate the molecular mechanisms that regulate the initiation of tooth formation, thus paving the way for in vitro tooth engineering. The objective of this proposal is to use mRNA and miRNA microarrays to identify the downstream target genes of Wnt/p-catenin signaling, and further analyze their roles and utilize them to induce teeth in vitro. In the Mentored phase (Aim 1), I will use laser capture microscopy to obtain tooth samples and to identify the downstream targets of Wnt/p-catenin signaling by comparing gene expression profiles of wild type mice with mice with epithelial loss of Ape or with constitutive activation of Pcatenin. The rationale for this approach is that a subset of genes expressed in these two transgenic mice should be similar. Therefore, only genes highlighted in both transgenic mice will be selected for further analysis. This training will expand my expertise in craniofacial biology, and the acquired knowledge in system bioinformatics and stem cell biology will facilitate my transition into a successful independent scientist. In the Independent phase, Aim 2 will focus on analyzing the role of candidate regulatory genes in tooth initiation using in vitro and in vivo approaches. In Aim 3, I will establish an in vitro culture system to recapitulate the non-cell autonomous effect of Wnt signaling, and will further manipulate the key regulatory genes to induce teeth in vitro. These studies, if successful, will provide fundamental insights into the development of teeth and other organs, and may also assist in tooth engineering in the clinic. Public Health Relevance: Loss of teeth leads to great physiological and psychological impairments. I will elucidate the molecular mechanisms underlying the induction of tooth formation, thus paving the way for in vitro tooth engineering.